In the connecting of a driving device, such as a motor, to a driven device, such as a piece of machinery, two procedures have been commonly used for producing such a coupling in a way that the driven member is driven only when the driving member is rotated in a given direction. One of these procedures is by the use of a ratchet, wherein a pawl hinged to the driving element engages steep surfaces of teeth on the driven element when the driving element is rotated in one direction and slide up sloping surfaces of the teeth when the driving element is rotated in the other direction. The other procedure is by use of a clutch in which the active element is a sprag which frictionally engages the driving and the driven elements by jamming when the driven element is driven in one direction, but which simply slides over the surfaces when the driven element is rotated in the other direction. Both of these procedures have inherent limitations. The ratchet is capable of exerting large driving forces or torque between the driven and the driving element, but it has a rather large increment of movement before it picks up the load, i.e., before the pawl engages a tooth. This increment may be as large a tooth distance. When one attempts to reduce this increment by making the teeth finer, the cross-sectional area of tooth available to transmit the torque (shear strength) is reduced. Furthermore, the hinge pin, spring, and sharp point associated with the pawl lead to wear and breakage. The spragtype coupling, on the other hand, has only a small increment of movement before it picks up the load, and in this respect, it is like a ratchet with an infinitely fine tooth; however, it transmits the power by friction and, therefore, the amount of power or torque that can be transmitted is limited by the friction that can be developed between surface of the sprag and the engaging surfaces of the input and output elements of the coupling. Another deficiency of the sprag coupling is the extreme wear that takes place when it is used for carrying starting and stopping loads. The sprag and the elements which it engages are formed of a hard material and considerable wear can take place. These and other difficulties experienced with the prior art uni-directional mechanisms have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of this invention to provide the uni-directional mechanism capable of transmitting large torque without an increment of non-power transmitting motion before load is picked up.
Another object of this invention is the provision of a uni-directional mechanism capable of connecting a driving device to a driven device which is capable of transmitting large torques with a minimum of wear to the operating parts.
A further object of the present invention is the provision of a uni-directional mechanism having the advantages of a ratchet clutch and a sprag clutch, but none of their disadvantages.
It is another object of the instant invention to provide a uni-directional mechanism wherein the transmittal of power takes place almost immediately at the start of motion at the driving device, which device is simple in construction.
It is another object of the instant invention to provide a uni-directional mechanism which can be inexpensively manufactured by conventional manufacturing methods and which is capable of a long life of useful service with a minimum of maintenance.